On resonant destabilization of toroidal Alfven eigenmodes by circulating and trapped energetic ions/alpha particles in tokamaks (original) (raw)

Toroidal Alfvtn eigenmodes are shown to be resonantly destabilized by both circulating and trapped energetic ions/alpha particles. In particular, the energetic circulating ions are shown to resonate with the mode not only at the AlfvCn speed (v,), but also at one-third of this speed, while for trapped ions, the dominant instability mechanism is shown to be due to the resonance between the precessional magnetic drift and the wave. Implications of the theory for present and future tokamaks are discussed. With the advent of next-generation fusion experiments which will focus on thermonuclear self-heating, it has become imperative to assess the potential of collective instabilities instigated by alpha particles. There are two classes of instabilities that are believed to be of serious concern to alpha-particle confinement: kinetic ballooning modes (KBM)'*2 and toroidal AlfvCn eigenmodes (TAE). lT3 These modes deserve special scrutiny because they are discrete in character [akBM e weip and arAE= v,/2qR, where o*;~ k,p,u,,/Lpi, Ls ' =-d In pi/dr is the bulk ion pressure scale length, pi=VtJni is the ion Larmor radius, VA=B/(h?lJti)